Although I agree with the idea that Frameworks can easily make your life worse instead of better. Especially at the time the Framework moves forward to a version that is not at all compatible with what you are doing.
Using API's that are not widely supported and then not relying on a well supported framework to abstract them, seems to me an even worse maintenance nightmare than sticking with a Framework.
However, in your update you are suggesting to use Object.observe as a simple alternative to React. I looked it up and https://developer.mozilla.org/en/docs/Web/JavaScript/Referen... says it is deprecated and even removed in some browsers.
Using API's that are not widely supported and then not relying on a well supported framework to abstract them, seems to me an even worse maintenance nightmare than sticking with a Framework.